Earthquakes do happen in Illinois, despite the state being far from any major tectonic plate boundary. Although the North American continent is a stable continental region, Illinois experiences seismic activity known as intraplate earthquakes. These events occur within the interior of a tectonic plate, not along its edges where most global seismic activity takes place. Residents of Illinois need to understand the underlying causes and the necessary steps for preparedness.
The Historical Record of Illinois Earthquakes
Illinois has a documented history of significant seismic events. The most powerful earthquakes ever recorded in the continental United States occurred in the winter of 1811–1812 along the New Madrid Seismic Zone, severely impacting the southern part of the Illinois Territory. This sequence included three major earthquakes, estimated between magnitude 7.0 and 8.0, and they were felt as far away as the East Coast. While the sparse population at the time limited the loss of life, a similar event today would cause widespread, catastrophic damage.
More recently, residents have felt notable, smaller events originating closer to home. The Wabash Valley Seismic Zone was the source of a magnitude 5.4 earthquake on April 18, 2008, with an epicenter near Mount Carmel, Illinois. This event caused minor structural damage and was felt across a wide area, including as far away as Canada. Another significant event was the magnitude 5.4 quake in 1968 centered near Dale, Illinois, which was felt in 23 states and caused considerable damage.
The Geological Mechanism of Intraplate Quakes
Intraplate quakes in Illinois are not caused by two plates grinding past each other, but rather by the transmission of stress through the interior of the North American Plate. This stress originates from plate tectonics, such as the slow, ongoing push from the Mid-Atlantic Ridge.
This stress accumulates until it finds a weak spot in the crust, often along ancient, buried geological features. The seismic zones affecting Illinois are associated with old, failed rifts—zones where the continent began to pull apart hundreds of millions of years ago but stopped. These ancient zones of weakness, such as the Reelfoot Rift, contain faults reactivated by the contemporary stress field. Because the crust in the central United States is thicker and colder than boundary regions, when a fault slips, the resulting ground shaking can travel much farther.
Major Seismic Zones Impacting Illinois
The primary seismic hazard for Illinois comes from two active regions: the New Madrid Seismic Zone (NMSZ) and the Wabash Valley Seismic Zone (WVSZ). The NMSZ is located in the Central Mississippi Valley and extends into the southernmost tip of Illinois near Cairo. This zone is associated with the massive 1811–1812 quakes, which had estimated magnitudes up to 7.7 or higher, and has a 25% to 40% chance of a magnitude 6.0 or greater earthquake occurring within a 50-year period.
The WVSZ is centered between southeastern Illinois and southwestern Indiana, posing a more direct threat to populated areas in the eastern part of the state. Geologic evidence suggests the WVSZ is capable of producing events with magnitudes up to 7.0–7.5. While the NMSZ generated the most powerful historical quakes, the WVSZ has been the source of the largest recent events with epicenters in Illinois, such as the 2008 Mount Carmel earthquake.
Personal and Community Preparedness
Preparing for an earthquake involves immediate safety measures and long-term mitigation efforts. During the shaking, the recommended procedure is “Drop, Cover, and Hold On.” This means dropping to the floor immediately, taking cover under a sturdy piece of furniture like a desk or table, and holding on until the shaking stops. If outdoors, move to an open area away from buildings, power lines, and trees.
For long-term safety, residents should secure heavy objects in their homes, anchoring bookshelves and water heaters to the walls. Assemble an emergency kit containing food, water, and supplies sufficient for a minimum of two weeks, as emergency responders may be overwhelmed after a major event. State and local governments promote preparedness by encouraging drills like the “Great Central U.S. Shakeout” and by adopting building codes that mandate greater infrastructure resilience.